5.0L (1979-1995) MustangTechnical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.
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Faulty Temp Sensor...Or Not?

I've been experiencing an issue with my 91 LX 5.0 with a fresh 347. I have an Autometer Temp Gauge ILO the Factory Gauge. I can start my car and once it gets to normal operating temperature, it will continue to creep up to overheating temps (as the gauge would show) but there's one kicker, my flex-a-lite black magic electric fan (on-board thermostat controlled) doesn't kick in and my 185 degree engine thermostat isn't opening thus leading me to believe its truly not overheating. I have used 2 different temp sensors with the same result. The one thing I haven't ruled out is the method of connection to the temp sensor on the intake. The original black rubber boot connector was severed and I used a butt connector and crimped an extension to an eyelet connector and fastened it to the sensor with 2 nuts. Could this be the culprit? Anyone else experienced this?

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The fan sensor is pushed in next to the upper hose outlet. Its odd because the temp gauge will creep up to 220 and then the engine thermostat will kick on along with the fan. I have also burped the system to make sure all the air pockets would be gone from the coolant. Any ideas?

If you are sure that your 185 thermostat is not opening then that is the problem.

If it don't open fully it will take a lot longer for the radiator to get to the temp to kick the fan on.

The gauge in the car gets up to 220 because it is taking the temp directly from the water jacket of the intake . So the engine temp is much hotter than the radiator because the thermostat is not opening.

Well, I thought I put the t-stats in correctly but it can't hurt me to double check. I have been getting my sensors off ebay so will also give autozone a shot. Thanks for your help, I do appreciate it.

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